The present invention is directed to optical fiber ribbons containing radiation cured encapsulating materials and is directed to radiation cured materials suitable for use, inter alia, as encapsulating materials for optical fiber ribbons. The radiation cured encapsulating materials have an advantageous combination of physical properties, including a low tear resistance and good adhesion. The radiation cured encapsulating materials in turn provide the optical fiber ribbons with improved reliability and versatility.
New optical fiber technologies are continually being developed to accommodate increasing demands for band width and other communication properties. Optical fiber ribbons have been developed to provide increased packing densities, improved accessibility and the like. In the U.S. telecommunications industry, 12-fiber ribbons have become a standard while in Japan, 8-fiber ribbons have commonly been employed. Optical fiber ribbons are disclosed, for example, in the Duecker U.S. Pat. No. 5,881,194, the Lochkovic et al U.S. Pat. No. 5,561,730 and the Hattori et al U.S. Pat. No. 5,524,164, and by McCreary et al, International Wire and Cable Symposium Proceedings (1998):432-439.
Generally, optical fiber ribbons comprise two or more optical fibers embedded and secured within a matrix material. The optical fibers are typically arranged in parallel relation substantially within a single plane. To accommodate increased capacity demands, as many as 24 optical fibers may be arranged in a single linear array in an optical ribbon. In certain applications, it is desirable to separate the optical fiber ribbon into two or more subunits by splitting the optical ribbon. To allow such separation, it has been a common practice to provide the optical fibers which are positioned at the ends of adjacent subunits in side-by-side direct contact with each other, without matrix material therebetween. This arrangement offers a convenient separating mechanism for splitting the optical fiber ribbon into subunits. However, owing to the small size of the individual fibers, their close proximity to one another, and/or the properties of the matrix materials, reliable splitting of the ribbon into subunits has been difficult as uneven tearing or splitting and/or optical fiber damage often results.
Several alternatives have been suggested to provide optical fiber ribbons which may be more reliably split into subunit ribbons. For example, notches have been provided in optical fiber ribbons along the desired tear or split line. In practice, the notches provided a weak area in the ribbon structure and have caused various problems with the handling integrity of the ribbons. Another alternative has been to provide modular subunits in an optical fiber ribbon. In this design, individual subunits are formed by embedding and securing a number of optical fibers in a matrix material. Two or more subunits are then embedded in an encapsulant material to form the optical fiber ribbon containing the modular subunit ribbons. For example, Hattori et al disclose optical fiber ribbon containing two modular subunit ribbons, each of which contains four optical fibers. The subunit ribbons are embedded and secured within an encapsulating material. Similarly, McCreary et al disclose a 24-fiber modular optical fiber ribbon which contains two 12-fiber subunit ribbons. The subunit ribbons are embedded within an encapsulating material to form the 24-fiber optical fiber.
While the modular type optical fiber ribbon containing subunit ribbons provide improvement over nonmodular optical fiber ribbons in various applications, the modular optical fiber ribbons typically exhibit one or more deficiencies in use. For example, during tearing or splitting of the modular subunits, uneven tear often occurs, resulting in overhang of the encapsulating matrix on one split subunit ribbon and excessive removal of encapsulating material on an adjacent subunit ribbon. The uneven tear or splitting of the encapsulating material can be particularly disadvantageous when the encapsulating material is provided with printed identification information and such information is removed from one of the subunits by uneven tearing. Previous modular optical fiber ribbons have also been known to exhibit delamination of the encapsulating material from the subunits, particularly upon the twisting of the optical fiber ribbons which is conventionally encountered in cabling applications. In yet additional modular optical fiber ribbons, cracking of the encapsulating material has occurred. Accordingly, the need remains for providing improved modular optical fiber ribbons which allow for reliable and even splitting of subunits therefrom and which exhibit improved handling robustness and resist cracking or delamination of the encapsulating material.
Accordingly, it is an object of the present invention to provide optical fiber ribbons, and particularly to provide optical fiber ribbons of the modular type wherein two or more subunit ribbons are encapsulated within an encapsulating material. It is an additional object of the present invention to provide optical fiber ribbons which overcome disadvantages of the prior art. It is a more specific object of the invention to provide optical fiber ribbons which allow reliable tearing or splitting of subunit ribbons and which exhibit robust handling properties and resist cracking and/or delamination of the encapsulating material. It is a further object of the invention to provide radiation cured encapsulating materials for use, inter alia, in modular optical fiber ribbons.
These and additional objects are provided by the optical fiber ribbons and encapsulating materials of the present invention. More particularly, the invention is directed to radiation cured encapsulating materials having a low tear resistance and good adhesion to an underlying surface. In a more specific embodiment, the encapsulating materials exhibit a tear resistance of less than about 2.20 pounds force and an adhesion force to an underlying surface of greater than about 0.0044 pounds force. In further preferred embodiments, the encapsulating material has a percent elongation at break of at least about 5% and a Young""s modulus at 25xc2x0 C. of at least about 1,000 psi. The present invention is also directed to optical fiber ribbons which comprise at least two optical fiber subunit ribbons encapsulated within a radiation cured encapsulating material, wherein the radiation cured encapsulating material has a low tear resistance which allows the subunit ribbons to be separated by hand, i.e., the ribbons exhibit hand separability of the subunit ribbons, and has robust handling properties, whereby the ribbons resist delamination and cracking when subjected to twisting. In a more specific embodiment, the optical fiber ribbons include an encapsulating material having a tear resistance of less than about 2.20 pounds force and an adhesion force to an outer surface of each subunit of greater than about 0.0044 pounds force. Preferably, the radiation cured encapsulating material in which the optical fiber subunit ribbons are encapsulated has a percent elongation at break of at least about 5% and a Young""s modulus at 25xc2x0 C. of at least about 1,000 psi.
The optical fiber ribbons according to the present invention are advantageous in that they allow reliable tearing or splitting of subunit ribbons therefrom, even by hand, resulting in even tear and preventing overhang or excessive removal of the encapsulating material in the individual split subunits. Additionally, the optical fiber ribbons of the invention exhibit robust handling properties and may be twisted in cabling environments without cracking of the encapsulating material or delamination of the encapsulating material from the subunit ribbons.
These and additional objects and advantages provided by the optical fiber ribbons and encapsulating materials of the present invention will be more fully apparent in view of the following detailed description.